Thermal Feedbacks Research Articles

Unraveling the Impacts of Submesoscale Thermal and Current Feedbacks on the Low Level Winds and Oceanic Submesoscale Currents

Abstract In this study, high-resolution coupled ocean-atmosphere simulations are performed over the Gulf Stream to investigate the influence of submesoscale (O(10 km)) thermal (TFB) and current (CFB) feedbacks on the low-level atmosphere and the oceanic submesoscale kinetic energy (SKE). At the submesoscale, TFB and CFB exhibit constructive and destructive effects on wind and surface stress, making this a more complex problem than for the mesoscale (O(100 km)). This co-influence alters classical coupling coefficients, posing a challenge to isolate individual coupling mechanisms. Here, the feedbacks are isolated separately by removing their imprint on the air-sea coupling fields in dedicated simulations. Both submesoscale TFB and CFB lead to a damping of the SKE. CFB causes eddy-killing by drag friction between currents and the atmosphere. However, while eddy-killing should be more efficient than its mesoscale counterpart due to a weaker wind response (less re-energization), its effect is hampered by an energization from TFB and by the highly transient nature of submesoscale flow, resulting in a modest 10% reduction in SKE. TFB also contributes to a reduction of SKE, mainly by causing a potential energy sink, associated with turbulent heat fluxes, especially at scales < 10km. The potential energy sink affects SKE through a decrease of baroclinic energy conversion, although this is slightly modulated by an increase in Ekman pumping by submesoscale CFB. Our results emphasize the importance of considering both TFB and CFB at the submesoscale, and highlight the limitations of mesoscale CFB parameterizations for submesoscale applications. Future parameterizations should be scale-aware and account for both TFB and CFB effects on momentum and heat fluxes.

Air–Sea Coupling Feedbacks over Tropical Instability Waves

Abstract Tropical instability waves (TIWs) are oceanic features that form around the equatorial Pacific cold tongue and influence the large-scale circulation and coupled climate variability including El Niño–Southern Oscillation. Local air–sea coupling over TIWs is thought to play an important role in the atmosphere and ocean’s energy and tracer budgets but is not well captured in coarse-resolution models. In this study, we isolate the impacts of TIW thermal (sea surface temperature–driven) and current (surface current–driven) feedbacks by removing TIW signatures in air–sea coupling fields in a high-resolution regional coupled model. The thermal feedback is found to damp TIW temperature variance by a factor of 2, associated both with the direct dependence of surface heat fluxes on SST (∼74%) and indirect impacts on surface winds (∼35%) and air temperature and humidity (∼−9%). These changes lead to cooling of the cold tongue SST by up to 0.1°C through reduced TIW-driven meridional heat fluxes and associated small changes in atmospheric circulation. The current feedback is decomposed into TIW (i.e., mesoscale) and mean (i.e., large-scale) components using separate experiments, with both having distinct impacts on TIWs and the mean state. The mesoscale current feedback reduces TIW eddy kinetic energy (EKE) by 22% through the eddy wind work, while the mean current feedback induces a further reduction of 8% by extracting energy from the mean currents and thus reducing barotropic EKE shear production. An improved understanding of small-scale tropical Pacific processes is needed to address biases in coarse-resolution models that impact their predictions and projections of Pacific climate variability and change. Significance Statement Tropical instability waves (TIWs) are oceanic features with ∼1000-km wavelengths that propagate westward on either side of the eastern equatorial Pacific cold tongue. TIWs drive lateral and vertical heat fluxes that impact several aspects of El Niño–Southern Oscillation. While climate models with a moderate, 1/4° ocean resolution can capture some TIW variability, they fail to properly represent many associated processes such as the impact of TIWs on the overlying atmosphere. Using sensitivity studies performed using a high-resolution regional coupled model, we study the impact of TIW air–sea coupling on the eastern Pacific climate system. Increased understanding of small-scale processes from studies such as this is essential to understand and address biases in models used for seasonal climate predictions and projections in the Pacific region.

Near-Surface Atmospheric Response to Meso- and Submesoscale Current and Thermal Feedbacks

Abstract Current feedback (CFB) and thermal feedback (TFB) have been shown to strongly influence both atmospheric and oceanic dynamics at the oceanic mesoscale (10–250 km). At smaller scales, oceanic submesoscale currents (SMCs; 0.1–10 km) have a major influence on the ocean’s energy budget, variability, and ecosystems. However, submesoscale air–sea interactions are not well understood because of observational and modeling limitations related to their scales. Here, we use a realistic submesoscale-permitting coupled oceanic and atmospheric model to quantify the spatiotemporal variability of TFB and CFB coupling in the northwest tropical Atlantic Ocean. While CFB still acts as a submesoscale eddy killer by inducing an energy sink from the SMCs to the atmosphere, it appears to be more efficient at the submesoscale by approximately 30% than at the mesoscale. Submesoscale CFB affects the surface stress, however, the finite time scale of SMCs for adjusting the atmospheric boundary layer results in a diminished low-level wind response, weakening partial ocean reenergization by about 70%. Unlike at the mesoscale, submesoscale CFB induces stress/wind convergence/divergence, influencing the atmospheric boundary layer through vertical motions. The linear relationship between the surface stress derivative or wind derivative fields and sea surface temperature gradients, widespread at the mesoscale, decreases by approximately 35% ± 7% or 77% ± 10%, respectively, at the submesoscale. In addition, submesoscale TFB induces turbulent heat fluxes comparable to those at the mesoscale. Seasonal variability in meso- and submesoscale CFB and TFB coupling is mostly related to background wind speed. Also, disentangling submesoscale CFB and TFB is challenging because they can reinforce or counteract each other.

Sub‐Mesoscale Wind‐Front Interactions: The Combined Impact of Thermal and Current Feedback

AbstractSurface ocean temperature and velocity anomalies at meso‐ and sub‐meso‐scales induce wind stress anomalies. These wind‐front interactions, referred to as thermal (TFB) and current (CFB) feedbacks, respectively, have been studied in isolation at mesoscale, yet they have rarely been considered in tandem. Here, we assess the combined influence of TFB and CFB and their relative impact on surface wind stress derivatives. Analyses are based on output from two regions of the Southern Ocean in a coupled simulation with local ocean resolution of 2 km. Considering both TFB and CFB shows regimes of interference, which remain mostly linear down to the simulation resolution. The jointly‐generated wind stress curl anomalies approach 10−5 N m−3, ∼20 times stronger than at mesoscale. The synergy of both feedbacks improves the ability to reconstruct wind stress curl magnitude and structure from both surface vorticity and SST gradients by 12%–37% on average, compared with using either feedback alone.

The Soil Moisture–Surface Flux Relationship as a Factor for Extreme Heat Predictability in Subseasonal to Seasonal Forecasts

Abstract Thresholds of soil moisture exist below which the atmosphere becomes hypersensitive to land surface drying, inducing thermal feedbacks that can exacerbate heatwaves. Realistic representation of threshold transitions in forecast models could improve extreme heat predictability and understanding of the role of land–atmosphere coupling. This study evaluates the performance of several forecast models from the Subseasonal Experiment (SubX) and several prototype versions of the Unified Forecast System (UFS) in their representation of threshold transitions by validation against reanalysis data. A metric of skill (true skill score) is applied to soil moisture breakpoint values, which mark the transition to heatwave hypersensitivity for drying soils. Forecast models have poor skill at being initialized on the correct side of the breakpoint, but show improvement when normalized to account for deficiencies in their soil moisture climatologies. Regionally, models performed best in the U.S. Northwest and worst in the Southwest. They effectively capture the tendency of western regions to spend more summer days in the hypersensitive regime than the eastern United States. Models represent well extreme heat as a consequence of atmospheric initial state for the first week of the forecast, but struggle to represent the soil moisture feedback regime. Forecast models generally perform better at extreme heat prediction when they are already dry and in the hypersensitive regime, even when erroneously so, implying that errors or biases exist in model parameterizations. Nevertheless, composite analysis shows encouraging model performance of the “hit” category, suggesting that an improvement in soil moisture initialization could further improve extreme heat forecast skill.

On the starting and operational transients at the core of the RMB based on 2D multigroup diffusion

RMB is a multipurpose reactor to be built by CNEN. As a multipurpose facility, unlike a nuclear power plant, some operations may result in transients, whether during the movement of materials from remote irradiation, extraction of neutrons through beam holes, reactor starting up, control rod accident, etc. For that, a methodology to visualize some variables like neutron fluxes, temperatures, power, etc., was developed. In this one present some preliminary results based on multigroup diffusion theory, thermal hydraulics feedbacks, and numerical methods, systematized in the DINUCLE code. DINUCLE couples a numerical code of multigroup spatial kinetics, for calculations of the flux of neutrons in the core of reactors, with a numerical code for the analysis of thermo hydraulic transients in rods and plates, considering the refrigerant always single-phase. Use was made of a programming in VBA (Visual Basic for Applications) from Excel, for data visualization in the transient.

Fast Human-in-the-Loop Control for HVAC Systems via Meta-Learning and Model-Based Offline Reinforcement Learning

Reinforcement learning (RL) methods can be used to develop a controller for the heating, ventilation, and air conditioning (HVAC) systems that both saves energy and ensures high occupants' thermal comfort levels. However, the existing works typically require on-policy data to train an RL agent, and the occupants' personalized thermal preferences are not considered, which is limited in the real-world scenarios. This paper designs a high-performance model-based offline RL algorithm for personalized HVAC systems. The proposed algorithm can quickly adapt to different occupants' thermal preferences with a few thermal feedbacks, guaranteeing the high occupants' personalized thermal comfort levels efficiently. Firstly, we use a meta-supervised learning algorithm to train an occupant's thermal preference model. Then, we train an ensemble neural network to predict the thermal states of the considered zone. In addition, the obtained ensemble networks can indicate the regions in the state and action spaces covered by the offline dataset. With the personalized thermal preference model updated via meta-testing, model-based RL is used to derive the optimal HVAC controller. Since the proposed algorithm only requires offline datasets and a few online thermal feedbacks for training, it contributes to a more practical deployment of the RL algorithm to HVAC systems. We use the ASHRAE database II to verify the effectiveness and advantage of the meta-learning algorithm for modeling different occupants' thermal preferences. Numerical simulations on the EnergPlus environment demonstrate that the proposed algorithm can guarantee personalized thermal preferences with a slight increase of power consumption of 1.91% compared with the model-based RL algorithm with on-policy data aggregation.

A model volcanic fissure with adjustable geometry and wall temperature

Fissure eruptions initiate with magma ascending and spreading through cracks in the ground that can extend for kilometres at the surface. Eruptions eventually localise to form one or a few persistent conduits and ultimately an array of discrete cones or craters. We built a new experimental apparatus to investigate the influences of fissure shape and wall-rock temperature on localisation within a volcanic fissure, and the thermal feedbacks associated with variability of these parameters. Our artificial fissure, or “Artfish,” has a slot geometry with adjustable shape and wall temperature. We can simulate both starting variability in fissure geometry and wall temperature, as well as changes in these parameters during an experiment to replicate, for example, blockage by wall-rock collapse, widening by wall-rock erosion, and warming by adjacent intrusions. We use polyethylene glycol (PEG 600) for our analogue fluid. A variable-speed pump allows for a range of fluid injection and ascent rates. Initial tests showcase the capabilities of the model and the types of data that may be acquired. Additional key features achieved include a stable and planar injection system, fluid recycling, and the use of particle tracers for monitoring flow patterns and velocities. The thermal evolution of the fluid-wall interface is quantitatively measured with thermal sensors, and the change in state of the PEG provides a clear visual indication of flow behaviour and solidification progress recorded on video. The potential experiments that can be conducted with this highly versatile model are numerous and will be used to gain a better understanding of the thermal controls on flow localisation and conduit development. This will assist hazard modellers to assess controls on eruption evolution and potentially to forecast sites where an initial fissure eruption may focus.

Effects of Quantity and Arrangement of a Flame-Retardant Cable on Burning Characteristics in Open and Compartment Environments

The results of cable burning experiments conducted in a well-controlled or open environment may differ from fire phenomena in an actual installation environment of cables where the effects of ventilation conditions and thermal feedback exist. In order to prevent the misunderstanding of fire phenomena due to these differences, the changes in burning characteristics in open and compartment environments were investigated for a flame-retardant (TFR-8) cable and general PVC (VCTF) cable arranged on three-layer trays. As a result, it was confirmed that the fire scale, fire spread area, and cable damage varied greatly depending on the cable arrangement under the same cable quantity condition. Furthermore, the maximum heat release rate (HRR) and fire growth rate of TFR-8 in the compartment environment increased more than 3-times compared to the open environment, and showed a similar level of fire risk to VCTF even though it is a flame-retardant cable. Additional experiments using vertical and horizontal openings of various shapes were conducted to evaluate the individual contributions of thermal feedbacks from the wall and smoke layer to the changes in burning characteristics within the compartment. The results of this study can be used as basic data to reduce fire damage while providing an essential understanding of cable fire phenomena.

Buffering of mantle conditions through water cycling and thermal feedbacks maintains magmatism over geologic time

The Earth has remained magmatically and volcanically active over its full geologic history despite continued planetary cooling and a lack of thermal equilibrium in the mantle. Here we investigate this conundrum using data-constrained numerical models of deep-water cycling and thermal history. We find that the homologous temperature - the ratio of upper mantle to melting temperatures - initially declined but has been buffered at a nearly constant value since 2.5-2.0 billion years ago. Melt buffering is a result of the dependence of melting temperature and mantle viscosity on both mantle temperature and water content. We show that thermal and water cycling feedbacks lead to a self-regulated mantle evolution, characterised by a near-constant mantle viscosity. This occurs even though the mantle remains far from thermal equilibrium. The added feedback from water-dependent melting allows magmatism to be co-buffered over geological time. Thus, we propose that coupled thermal and water cycling feedbacks have maintained melting on Earth and associated volcanic/magmatic activity.

Hysteresis of the Glacial Atlantic Meridional Overturning Circulation Controlled by Thermal Feedbacks

AbstractThe multiple equilibrium behavior of the Atlantic meridional overturning circulation (AMOC) is related to the mode transition of the AMOC, which played an important role in abrupt glacial climate changes. However, the difference between modern and glacial climates is not well understood. Here, we examined the structure of the multiple equilibria of the AMOC under the modern and glacial climates through hysteresis experiments using an earth system model of intermediate complexity. The glacial AMOC exhibited a shallower AMOC mode but not the off mode, and a narrower range of multiple equilibria than the modern AMOC. This glacial hysteresis behavior occurred associated with a shift of deep water formation due to changes in surface air temperature and sea ice, whereas that of the modern AMOC is attributed to the basin‐scale salinity feedback. These features were commonly found in two glacial simulations with different strengths of the AMOC at the Last Glacial Maximum.

Long-term climate-influenced land cover change in discontinuous permafrost peatland complexes

Abstract. The discontinuous permafrost zone is undergoing rapid transformation as a result of unprecedented permafrost thaw brought on by circumpolar climate warming. Rapid warming over recent decades has significantly decreased the area underlain by permafrost in peatland complexes. It has catalysed extensive landscape transitions in the Taiga Plains of northwestern Canada, transforming forest-dominated landscapes to those that are wetland dominated. However, the advanced stages of this landscape transition, and the hydrological and thermal mechanisms and feedbacks governing these environments, are unclear. This study explores the current trajectory of land cover change across a 300 000 km2 region of northwestern Canada's discontinuous permafrost zone by presenting a north–south space-for-time substitution that capitalizes on the region's 600 km latitudinal span. We combine extensive geomatics data across the Taiga Plains with ground-based hydrometeorological measurements collected in the Scotty Creek basin, Northwest Territories, Canada, which is located in the medial latitudes of the Taiga Plains and is undergoing rapid landscape change. These data are used to inform a new conceptual framework of landscape evolution that accounts for the observed patterns of permafrost thaw-induced land cover change and provides a basis for predicting future changes. Permafrost thaw-induced changes in hydrology promote partial drainage and drying of collapse scar wetlands, leading to areas of afforestation forming treed wetlands without underlying permafrost. Across the north–south latitudinal gradient spanning the Taiga Plains, relatively undisturbed forested plateau–wetland complexes dominate the region's higher latitudes, forest–wetland patchwork are most prevalent at the medial latitudes, and forested peatlands are increasingly present across lower latitudes. This trend reflects the progression of wetland transition occurring locally in the plateau–wetland complexes of the Scotty Creek basin and informs our understanding of the anticipated trajectory of change in the discontinuous permafrost zone.

Coupled hydrological and geochemical impacts of wildfire in peatland-dominated regions of discontinuous permafrost

Naturally-ignited wildfires are increasing in frequency and severity in northern regions, contributing to rapid permafrost thaw-induced landscape change driven by climate warming. Low-severity wildfires typically result in minor organic matter loss. The impacts of such fires on the hydrological and geochemical dynamics of peat plateau-wetland complexes have not been examined. In 2014, a low-severity wildfire, with minimal ground surface damage, burned approximately one-half of a 5 ha permafrost plateau in the wetland-dominated landscape of the Scotty Creek watershed, Northwest Territories, Canada, in the discontinuous permafrost zone. In March 2016, hydrometeorological and permafrost conditions on the burned and unaffected plateaus were monitored including snowpack characteristics and surface energy dynamics. Pore water samples were collected from the saturated layer as thaw progressed throughout the growing season on the burned and unaffected plateaus. Repeated probing of the frost table depth was coupled with laboratory analyses of peat physical and hydraulic characteristics performed on peat cores collected from the top 20 cm of the ground surface in the burned and unaffected plots. The higher transmissivity of the burned forest canopy accelerated snowmelt promoting earlier onset of the thawing season and increased the ground heat flux to melt ground ice. Wildfire increased the thickness of the supra-permafrost layer, including the active layer and talik, resulting in a more uniform subsurface with limited depressional storage capacity and reduced preferential runoff flowpaths across the burned plateau. The incorporation of ash and char into the peat matrix reduced pore diameters, promoting greater subsurface soil moisture retention and longer pore water residence times ultimately providing greater opportunity for soil-water interaction and biogeochemical reactions. Consequently, pore water showed elevated dissolved solutes, dissolved organic matter and mercury concentrations in the burned site. Low-severity wildfires have the potential to trigger a series of complex, inter-related hydrological, thermal and biogeochemical processes and feedbacks.

THE McSAFE PROJECT - HIGH-PERFORMANCE MONTE CARLO BASED METHODS FOR SAFETY DEMONSTRATION: FROM PROOF OF CONCEPT TO INDUSTRY APPLICATIONS

The increasing use of Monte Carlo methods for core analysis is fostered by the huge and cheap computer power available nowadays e.g. in large HPC. Apart from the classical criticality calculations, the application of Monte Carlo methods for depletion analysis and cross section generation for diffusion and transport core simulators is also expanding. In addition, the development of multi-physics codes by coupling Monte Carlo solvers with thermal hydraulic codes (CFD, subchannel and system thermal hydraulics) to perform full core static core analysis at fuel assembly or pin level has progressed in the last decades. Finally, the extensions of the Monte Carlo codes to describe the behavior of prompt and delay neutrons, control rod movements, etc. has been started some years ago. Recent coupling of dynamic versions of Monte Carlo codes with subchannel codes make possible the analysis of transient e.g. rod ejection accidents and it paves the way for the simulation of any kind of design basis accidents as an alternative option to the use of diffusion and transport based deterministic solvers. The H2020 McSAFE Project is focused on the improvement of methods for depletion considering thermal hydraulic feedbacks, extension of the coupled neutronic/thermal hydraulic codes by the incorporation of a fuel performance solver, the development of dynamic Monte Carlo codes and the development of methods to handle large depletion problems and to reduce the statistical uncertainty. The validation of the multi-physics tools developed within McSAFE will be performed using plant data and unique tests e.g. the SPERT III E REA test. This paper will describe the main developments, solution approaches, and selected results.

On the inherent load following features of a small modular nuclear reactor

Small modular reactors (SMR) are deemed to largely participate in the midterm electricity production owing to their remarkable operational features. Among all, the coordinated employment of in-built design characteristics to procure enhanced safety and sustainability objectives is a key advantage. Inherent load following aspects of the NuScale integral design of SMRs will thus be explored in this work. To this end, a reasonably accurate coupled dynamic modeling platform is developed which accompanies the thermo-neutronic phenomena in the reactor core alongside with the heat transfer to the steam generator. Turbine leading (reactor following) operation is investigated as the load cycling strategy which largely relies on the role of thermal reactivity feedbacks in the reactor core to accommodate for the power demand scheduled from the turbine side. Comprehensive sensitivity analysis is conducted to figure out the opposing behavior of the fuel and coolant feedbacks in this regard. In line with the delaying act of the plant cold leg (connecting the reactor core and the steam generator), these results would help more appropriately occasion inherent load following features especially at the design stage, thus enabling more rapid load following scenarios in small modular reactors.

Distinct responses of Asian summer monsoon to black carbon aerosols and greenhouse gases

Abstract. Black carbon (BC) aerosols emitted from natural and anthropogenic sources induce positive radiative forcing and global warming, which in turn significantly affect the Asian summer monsoon (ASM). However, many aspects of the BC effect on the ASM remain elusive and largely inconsistent among previous studies, which is strongly dependent on different low-level thermal feedbacks over the Asian continent and the surrounding ocean. This study examines the response of the ASM to BC forcing in comparison with the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver Response Model Intercomparison Project (PDRMIP) simulations under an extremely high BC level (10 times modern global BC emissions or concentrations, labeled BC×10) from nine global climate models (GCMs). The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P−E; a 13.6 % increase for BC forcing and 12.1 % for GHGs from the nine-model ensemble, respectively), there exists a much larger uncertainty in changes in ASM P−E induced by BC than by GHGs. The summer P−E is increased by 7.7 % to 15.3 % due to these two forcings over three subregions, including East Asian, South Asian and western North Pacific monsoon regions. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P−E induced by BC and GHGs. The change in ASM P−E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation, whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor. Radiative forcing of BC significantly increases the upper-level atmospheric temperature over the Asian region to enhance the upper-level meridional land–sea thermal gradient (MLOTG), resulting in a northward shift of the upper-level subtropical westerly jet and an enhancement of the low-level monsoon circulation, whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature, which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation. Hence, our results indicate a different mechanism of BC climate effects under the extremely high BC level: that BC forcing significantly enhances the upper-level atmospheric temperature over the Asian region, determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

Nonlinear stability analysis of a self-pressurized, natural circulation integral reactor via the Lyapunov's second method

The non-linear stability of a small modular self-pressurized reactor is assessed here by means of a direct Lyapunov function. The trial and error method is analyzed by applying an appropriate dynamical model for this type of reactors. A function containing all the states of the system which has conditions of a direct Lyapunov function is presented. This continuous function is positive definite and its derivative is negative semi-definite. The results indicate that the primary coolant is asymptotically global stable over its entire power range. Also, we assess the effects of neutronic and thermal hydraulic feedbacks on the system stability. Its been found that in the presence of these feedbacks, the system is stable in the entire power range.

Primary Drivers of Reptile Overwintering Habitat Suitability: Integrating Wetland Ecohydrology and Spatial Complexity

AbstractIdentifying ecosystems resilient to climate and land-use changes is recognized as essential for conservation strategies. However, wetland ecosystems may respond differently to stressors depending on their successional state and the strength of ecohydrological feedbacks resulting in fluctuations in habitat availability and suitability. Long-term habitat suitability is necessary for the persistence of wetland-dependent species and a key characteristic of climatic refugia. In the present article, we review and synthesize biogeochemical, thermal, ecological, and hydrological feedbacks and interactions that operate within wetlands and, consequently, regulate overwintering suitability for many freshwater turtles and snakes. We propose that understanding the breadth and interconnected nature of processes controlling temperature, dissolved oxygen, and water table position are vital for the conservation of northern reptile populations that depend on wetlands to survive winter conditions. Finally, we suggest that our integrated framework can guide future research and the management of wetland ecosystems in an era of unprecedented change.

Estimating the influence of thermal inertia and feedbacks in the atmosphere–ocean system on the variability of global surface temperature

The present climate is characterized not only by the trend due to the increase in the concentrations of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability, calculated via the computational results from the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program, show significant inter-model differences. In particular, inter-model distinctions in decadal anomalies of the global and hemispheric temperatures reach four times the value. However, unlike the inter-model differences in climate sensitivity, the reasons for a wide range of estimates of climate variability are still unclear. Based on the two-component energy-balance stochastic model, the paper analyzes the inter-annual and inter-decadal variability of the mean global surface temperature (GST) to feedback and the thermal inertia of the atmosphere-ocean system, assuming that the external forcing is random fluctu-ations of the radiation balance at the top of the atmosphere. Using the obtained ab-solute and relative sensitivity functions, the influence of thermal inertia and feed-backs in the climate system on the inter-annual and inter-decimal variability (variance) of the GST and its spectrum is estimated.

Estimating the Influence of Thermal Inertia and Feedbacks in the Atmosphere–Ocean System on the Variability of the Global Surface Air Temperature

The modern climate of our planet is characterized not only by a trend caused by an increase in the concentration of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability based on the modeling results of the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program is characterized by significant differences between models. In particular, for the decadal-scale anomalies of the global and hemispheric temperatures, the standard deviation differences between models are as high as fourfold. However, in contrast to the differences in climate sensitivity between models, the causes of a wide range of the estimates of climate variability are still not entirely understood. The research in this paper is based on two-component energy-balance stochastic model. We analyze the sensitivity of interannual and interdecade variability of the mean global surface temperature (GST) to the feedback and thermal inertia of the atmosphere–ocean system under the assumption that the main external forcing factor is random fluctuations of the radiation balance at the upper boundary of the atmosphere. We estimate the influence of thermal inertia and feedback in the climate system on the interannual and interdecade variability (variance) of the GST and the spectrum of its fluctuations using the absolute and relative sensitivity functions derived in the research.